1. Field of the invention
The present invention relates to a display device used in television receivers, computer terminal displays, and similar apparatuses.
2. Description of Related Art
The envelope with glass screen (hereinafter called as an envelope) of a display device, wherein electron beams are used to make phosphor illuminate, thereby displaying picture images, is required to satisfy the conditions of a vacuum vessel.
The envelope of the prior art is made entirely of glass including the front section provided with the fluorescent screen on the inner surface thereof, both side sections, top section, bottom section and rear section, in a constitution satisfactory in terms of reliability. However, the envelope made of glass is liable to cause delayed fracture by the stress generated by making the inner space vacuum, eventually leading to breakage. This problem may be countered by choosing a proper thickness for the glass wall, although this leads to an increase in the weight of the entire envelope which contradicts the trend toward less weight of products.
Another method of preventing the delayed fracture is to use glass only in the front section of the envelope and make the other parts with a metal. Because the use of a metal decreases a possibility of delayed fracture to occur, there is no need to increase the wall thickness as in case of glass, and therefore the weight of the device can be decreased.
FIG.1 is a perspective view illustrative of only the envelope of a flat type display device. FIG. 2 is a schematic longitudinal sectional drawing of the portion cut by line II--II. The envelope comprises a front section 1 including a glass panel provided with a fluorescent screen on the inner surface thereof and other parts made of a metal, that are both side sections 5, 5, a top section 2, a bottom section 3 and a rear section 4. The envelope has inner components such as electrodes to produce picture images being installed therein, however, they are not shown in the drawing.
The glass is the cathode ray tube material H5702 specified by the Electronic Industries Association of Japan, for example, and is made in height/width ratio of 3/4 and diagonal screen size of 20 inches. The metallic material is cord-rolled steel #430. Thickness T1 of the glass panel of the front section 1 is 26.4 mm, thickness T2 of the metal sheet on the four circumferential sections (both side sections 5, 5, top section 2, bottom section 3) is 5.5 mm, and thickness T3 of the metal sheet on the rear section 4 is 5.5 mm, and depth D of the envelope formed by the front section 1 and the rear section 4 is 60 mm. Weight of this constitution is 25.9 kg.
Joint A in the front section 1 between the glass panel and the metal sheet forming the four circumferential sections will now be described below. FIG. 3 and FIG. 4 are enlarged views illustrative of two examples of the joint A. In the constitution shown in FIG. 3, the glass panel 1a has a groove on the edge thereof to allow the metal sheet to be inserted therein. An end of the metal sheet 2a constituting the top section 2 is bent toward the front section and is inserted into the groove. The metal and glass of the joint are bonded by fusing. In the constitution shown in FIG. 4, metal sheet 2a bent toward the front section similarly to that of FIG. 3 and the edge of the glass panel 1a are placed on one another and are bonded by means of frit glass 6.
FIG. 5 is a schematic longitudinal sectional drawing illustrative of an envelope of a display device which is made lighter than the display device shown in FIG. 1, FIG. 2. The envelope is made in rounded shape to reduce the stress and thereby making it possible to reduce both the thickness and the weight. Radius of curvature R1 of the front section 1 is 1738 mm, radius of curvature R2 of the top and bottom sections 2, 3 is 30 mm, and radius of curvature R3 of the rear section 4 is 884 mm. T1 is 16.0 mm, T2 is 2.4 mm and T3 is 1.0 mm, and weight of this constitution is made as small as 10.3 kg. The stress generated by pumping out the envelope to make the inside vacuum is 1 kgf/cm.sup.2 in the front section 1 made of glass, and 15 kgf/cm.sup.2 in sections made of the metal. However, depth D becomes 20+60+40=120 mm because the front section 1 and the rear section 4 are made to protrude toward the outside of the envelope.
As described above, changes in the depth and in weight of a display device, namely an envelope, are in a contradictory relationship in the conventional device, and it has been difficult to decrease the weight and depth simultaneously.